src/Pure/Syntax/syntax_ext.ML

--- a/src/Pure/Syntax/syntax_ext.ML	Mon Oct 21 22:58:14 2024 +0200
+++ b/src/Pure/Syntax/syntax_ext.ML	Tue Oct 22 12:03:46 2024 +0200
@@ -383,7 +383,7 @@
       else
         let
           val indexed_const =
-            if const <> "" then const ^ "_indexed"
+            if const <> "" then Lexicon.mark_indexed const
             else err_in_mixfix "Missing constant name for indexed syntax";
           val rangeT = Term.range_type typ handle Match =>
             err_in_mixfix "Missing structure argument for indexed syntax";